Poor booking service and no availability of spare parts

I booked Monday for the car to be brought in for Thursday gearbox seal repairs. And the booking was confirmed same day. Thursday I dropped the car off in the afternoon they phone and tell me they didnt repair the car because they don't have stock. I mean I booked for this repairs already on Monday why was the booking confirmed same day if they didn't have stock?

Now I can't fetch the car and it has to sleep at the dealership and hoping by Friday dat so called parts will arrive. Such inconvenience